1. Field of the Invention
The present invention relates to a process for controlling an internal combustion engine and, more specifically, to a process using a model of the engine to define the commands to be applied in order to obtain a desired result.
Modern techniques for controlling internal combustion engines of motor vehicles place increasing reliance on mathematical modeling of the engines to produce more robust control processes capable of more accurately taking account of requirements imposed by drivers of the motor vehicles and of the constraints imposed by pollution-control regulations. Mathematical models enable output variables y of an engine to be estimated using a set of commands u that is input to the engine. For example, the model depicted in block form in FIG. 1, enables a set of commands u such as the set formed by the throttle position TPS, the position EGRV of an exhaust gas recirculation valve, the ignition advance IGA, the amount INJ of the fuel injected, etc., to be used to estimate output variables y of the engine such as the torque TQ supplied, the amount of air drawn in MAF, the richness LAM of the exhaust gases, and their recirculation rate EGR. These output variables cannot always be measured directly and economically on an actual engine.
FIG. 2 depicts, in simplified form, a known process for controlling an internal combustion engine. Such a process is known, for example, from French patent application 9700648 filed by the assignee of the present application. A set-point torque TQ_SP is determined by evaluating the depression of a throttle pedal. A set of commands u to be applied to means 11 for adjusting the engine 1 is determined by applying the set-point torque TQ_SP to an inverse model M.sup.-1 of the engine. Other set points LAM_SP and EGR_SP that might be present can also be applied to the inverse model. However, an inverse model of this kind needs to be obtained by an analytical inversion of the direct model M shown in FIG. 1, which, in the case of multi-variable models (multiple inputs and multiple outputs) is an extremely complex operation. Furthermore, the various coefficients of the analytical equations that form the direct model are generally obtained experimentally by identifying the model with the actual engine. The coefficients are stored in numerous mapping tables. When the direct model is inverted, these tables have to be inverted and, given the non-linearity of the coefficients, this often leads to indeterminacy or inaccuracies which are prejudicial to the effectiveness of the control process. Furthermore, any modification to the direct model, even to just one coefficient, necessitates a further complete inversion of the model. Thus development and optimization is extremely lengthy and expensive.